Abstract
M.Tech.
Photodynamic therapy is a treatment that is used for the destruction of certain types of tumours and is emerging as a promising treatment modality in the field of dermatology (Davids et al., 2008). The photochemical interactions of the photosensitizer, light and molecular oxygen producing reactive oxygen species known as ROS, results in damage to organelles within malignant cells and so can lead to tumour destruction (Plaetzer et al., 2008).
Melanoma is one of the most common forms of malignancies (Oliveria et al., 2007). Unfortunately, there are limited treatment options available for this disease because chemotherapy and radiation therapy are largely ineffective. Metastatic disease frequently develops even after potentially curative surgery (MacCormack, 2008). Since this metastatic disease is an understudied cancer, and the incidence and mortality is increasing, describing the long term burden of this cancer and identifying factors that contribute to it will facilitate efforts to develop responsive prevention strategies, so that novel therapies such as PDT can be proposed (Oliveria et al., 2007; Pan et al., 2008; Schuitmaker et al., 1996).
Numerous worldwide clinical trials have shown that PDT represents an effective and safe modality for various skin disorders, but little research has been done in terms of its effect on malignant melanomas (De Rosa and Bentley, 2000; Kolarova et al., 2008). In order for PDT to be an effective treatment modality it depends on many factors such as the type of photosensitizer utilized its ability to selectively penetrate tumour cells and the duration of the treatment (Robertson et al., 2009). Other important factors include the type of activating light source, its ability to penetrate the desired target and the duration of exposure (Plaetzer et al., 2008). Lastly, the type of target cells and their oxygen status also play an important role in the efficacy iv
of PDT (Kolarova et al., 2008). In order for PDT to be completely effective, the resulting damage from the treatment must surpass cellular repair mechanisms and cause direct destruction of cellular pathways through vascular compromise and increase immune response to overcome disease (Pazos and Nader, 2007). Porphyrins are the most studied photosensitizers and their disadvantage is the inability to specifically localize in tumour cells and so they are retained in normal cells for prolonged periods, causing patients to be photosensitive (Braathen et al., 2007). This factor stimulated the development of second generation photosensitizers with improved physical, chemical and spectral properties (Davids et al., 2008). Phthalocyanine compounds are second generation photosensitizers which have shown potential in the PDT treatment of many cancers (Kolarova et al., 2007).